Roof Pitch Calculator

Enter whichever one you have (a rise over a run, an angle, or a percent grade). You get the other two, plus the multiplier that turns flat footprint area into the roof area you actually cover.

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This is a general measurement calculator. Confirm dimensions, product coverage and job requirements before ordering or installing materials.

Pitch, angle and grade are one fact written three ways

A pitch is a ratio: how far the roof climbs for every 12 units it travels sideways. Six in twelve, 26.57 degrees and a fifty percent grade are not three different measurements. They are three notations for the same slope, and a roof gets described in all three depending on who is talking: a framer, an engineer or a survey. Converting between them is trigonometry, so this does it exactly rather than reading it off a chart.

The number worth carrying away is the pitch multiplier. It is the square root of rise squared plus run squared, divided by the run, and it is what a flat footprint has to be multiplied by to become the surface someone walks on and covers. A six in twelve roof multiplies by about 1.118, so a hundred square feet of footprint is nearly a hundred and twelve square feet of roof. Ignore it and you are short on every roof you ever order for.

The mistake that costs the most is measuring the run along the rafter instead of level. The run is horizontal, always. The slope distance is what you are solving for, not what you feed in. Get those two the wrong way round and the pitch comes out shallow and the multiplier comes out low, which is the direction that leaves you short rather than over.

The other thing to know is where the multiplier does not apply. It converts footprint area only, so overhangs, dormers and anything measured on the slope already are separate. Write the pitch down while the ladder is still up. In Zeus it goes on that address, and the next visit starts from a measured number instead of a second climb.

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